Chronic and/or neuropathic pain after nerve injury is a major health problem worldwide. Neuropathic pain (NP) is caused by a primary lesion or disease of the somatosensory system (Jensen T S, Baron R, Haanpaa M, et al. A new definition of neuropathic pain. Pain 2011; 152:2204-5). Not uncommonly, its severity, chronicity and the poor side-effect to benefit ratio of current pharmacotherapy for NP (Dworkin R H. An overview of neuropathic pain: syndromes, symptoms, signs, and several mechanisms. Clin J Pain 2002; 18:343-9; Finnerup N B, Sindrup S H, Jensen T S. The evidence for pharmacological treatment of neuropathic pain. Pain 2010; 150:573-81) lead to severely impaired physical and psychological functioning among sufferers (Jensen M P, Chodroff M J, Dworkin R H. The impact of neuropathic pain on health-related quality of life: review and implications. Neurology 2007; 68:1178-82). In the general population, the incidence of NP is estimated to be 1% (Dieleman J P, Kerklaan J, Huygen F J, Bouma P A, Sturkenboom M C. Incidence rates and treatment of neuropathic pain conditions in the general population. Pain 2008; 137:681-8) and rising (Dworkin, supra). The resulting prevalence of moderate to severe chronic NP is 5% (Bouhassira D, Lanteri-Minet M, Attal N, Laurent B, Touboul C. Prevalence of chronic pain with neuropathic characteristics in the general population. Pain 2008; 136:380-7), making it a common and formidable health problem worldwide.
Despite the numerous etiologies of NP, the mechanism of its perpetuation, regardless of origin, appears to involve the interaction of neuronal, glial and immune cells (Scholz J, Woolf C J. The neuropathic pain triad: neurons, immune cells and glia. Nat Neurosci 2007; 10:1361-8). Communication between these cells has been attributed to signaling via the family of mitogen-activated protein kinase (MAPK) proteins (Ji R R, Gereau R Wt, Malcangio M, Strichartz G R. MAP kinase and pain. Brain Res Rev 2009; 60:135-48).
Neuropathic pain is a complex, chronic pain state that usually is accompanied by tissue injury. With neuropathic pain, the nerve fibers themselves may be damaged, dysfunctional or injured. These damaged nerve fibers send incorrect signals to other pain centers. The impact of nerve fiber injury includes a change in nerve function both at the site of injury and areas around the injury. Some neuropathic pain studies suggest the use of non-steroidal anti-inflammatory drugs, such as Aleve or Motrin, may ease pain. Some people may require a stronger painkiller, such as those containing morphine. Anticonvulsant and antidepressant drugs seem to work in some cases. If another condition, such as diabetes, is involved, better management of that disorder may alleviate the pain.
In cases that are difficult to treat, a pain specialist may use invasive or implantable device therapies to manage the pain. Electrical stimulation of the nerves involved in neuropathic pain generation may also control the pain symptoms.
Unfortunately, neuropathic pain often responds poorly to standard pain treatments and occasionally may get worse instead of better over time. For some people, it can lead to serious disability. Current treatments are characterized by an unsatisfactory side effect to benefit-ratio.
Thus, additional therapies that target neurological disorders such as neuropathic pain are urgently needed.